Question When coupling a trailer: Answers Make sure to couple matching glad hands. Any glad hand can be connected to any other glad hand. It is best to leave one glad hand unattached. Only one set of glad hands should be connected. Explanation When coupling, make sure you couple matching glad hands. They are often color-coded to help drivers avoid mistakes. Typically, blue is used for service lines and red is used for emergency lines. Take a FREE Practice Test Now This questions appears in the following tests: Alabama Combination , Georgia Combination , Illinois Combination , New York Combination , North Dakota Combination , South Carolina Combination ,